With 2-acrylamido-2-methylpropane sulfonic acid (AMPS）and acrylamide (AM）as raw materials, a water-soluble AM/AMPS copolymer is prepared. The factors effecting flocculation, such as the ratio of monomers, the amount of initiator, reaction temperature and reaction time have been investigated to obtain optimal polymerization condition. The optimal synthetic condition to flocculation is that reaction time is 7 h, m(AM)∶m(AMPS）equals 7∶3, reaction temperature is 45℃, the mass fraction of the reaction initiator, i.e. ammonium persulfate is 0.02% and pH is 6~8. The results show that the copolymer flocculant has good performance in resisting heat and salt.